How to build skyscrapers
But not only security concerns temporarily slowed architects and investors. Even before the New York attacks, immense technical hurdles faced new heights. Many questions had to be answered:
How do 800 meter high buildings withstand the enormous wind pressure that makes them sway up to three meters? How do you give such heavyweight giants a firm footing in soft ground? How do you pump the concrete up fast enough before it begins to harden? How do thousands of residents and visitors get into their homes or offices in a reasonable amount of time every day? How do the necessary elevators have to be arranged so that they take up as little valuable space as possible?
When the problems are so huge, architects like to dream of a client with a thick wallet and an oversized ego, someone like the US real estate tycoon Donald Trump. In spring 2001 he hired the Chicago architectural office SOM. The renowned team, which among other things had built the Sears Tower in Chicago, was to build the tallest building in the world for Trump - 700 meters and 160 stories high. The decisive meeting was to take place on September 11, 2001. The collapse of the Twin Towers ruined the grandiose plans. Instead, a miniature edition with only 92 floors is now being built in Chicago.
But structural engineer Bill Baker and architect Adrian Smith from SOM never let go of the topic - they were striving for higher things. For a residential building with 90 floors in Seoul, the Tower Palace III, they developed a Y-shaped floor plan for the first time in order to achieve a maximum number of windows per apartment. As the structural engineer Baker found, the basic shape not only brought more light into the building, it also made it wind-stable and incredibly light. Because each of the three wings supports its two neighbors. If the wind blows against one pillar, the one behind it remains unloaded and thus stabilizes the high-rise.
The only catch of the construction: At heights of 700 meters and more, the house would swing powerfully under the wind pressure and make its residents seasick. To prevent this from happening, Baker and Smith firmly connected the three wings to the core of the building. Now Smith and Baker were certain: "This is the way it could work."
The opportunity to test the concept soon arose: In the spring of 2003, Smith and Baker were sitting in Manhattan across from two developers from Dubai who represented the Emaar company. They had no less in mind than to erect the tallest building in the world with the blessing of the ruling Sheikh Mohammed bin Rashid al-Maktoum and the means of the royal family. The Burj Dubai got higher with every meeting: the declared goal was to outstrip the 101 Tower in Taipei.
Around $ 1.8 billion was made available for the project. A completely new district is to be built around the tower - Downtown Dubai with 320,000 luxury apartments, offices, parks and an artificial lake. It is to be built in the traditional Arabic style and exude an oriental flair where a few years ago there was nothing but sand and sun. The royal family wants to create tourist attractions for the time after the oil wells have dried up. As early as 2010, this source of income for Dubai could be largely exhausted.
The project is an immense challenge for the architects, engineers and structural engineers involved. Dubai is not an earthquake area, but the desert wind Shamal, which can blow at up to 200 km / h, is a serious danger for high-rise buildings. The engineers therefore spent a long time working on the structure of the skyscraper in the wind tunnel on a model on a scale of 1: 200. The result: the tower is given a round shape that offers little attack surface for storms. 26 terraces weaken and divert the wind. Reinforcements in the lower floors also make the tower extremely torsion-resistant.
A lot of technology from Germany is used to build the giant in the desert. Bauer Spezialtiefbau from the Bavarian town of Schrobenhausen ensures that it is firmly established. The specialists rammed 800 concrete piles up to 50 meters deep into the sand and connected them with a 7000 square meter concrete slab to form a stable foundation.
Putzmeister AG from the Swabian Aichtal solved one of the most pressing problems. The challenge: How does the special concrete get quickly from the mixer on the ground to a lofty height? The classic method - pouring the concrete in buckets and using cranes to pull it up - would have cost too much time.
The resourceful Swabians therefore developed their own pipe conveyor system for the high-rise project with special pipe guides for easy replacement of damaged pipes and three high-performance pumps. It works so well that the inventors have applied for a patent for the system. Around 30 cubic meters of concrete can be pressed to a height of 600 meters in one hour. The flexibly suspended riser pipes are eleven millimeters thick so that they can withstand the mechanical stresses caused by gravel and water. An ultrasound device regularly checks the wall thickness, which decreases with every hour of operation because the gravel-water mixture acts like sandpaper.
The concrete used on the Burj Dubai is a special recipe. Not only does it have four times the compressive strength of normal concrete. It sets even two hours after mixing. It takes almost 20 chemical additives to keep it pumpable and flowable. In order for the concrete to get into the formwork in summer at outside temperatures of 50 degrees Celsius with a maximum of 30 degrees, it also has to be cooled with ice, which replaces part of the water. In any case, concreting is only done at night during the hot season. During the day, the iron benders and formworkers are at work - or the crane assembly team lifts the three cranes on the roof of the building shell one floor up again. With this ingenious logistics it is possible to complete a new floor every three days.
The greatest precision is required when assembling the shiny silver aluminum facade, which protects the building from wind, rain, sun and sandstorms. A medium-sized company from Langenfeld near Düsseldorf has the necessary specialist knowledge. World market leader Halfen supplies the fastening rails for the facade elements, which can be latched quickly and precisely without drilling. “A Halfen rail saves you having to drill 20 holes,” says managing director Hans-Dieter Hardt. The rails are already concreted in during construction. They are dimensioned in such a way that they can withstand enormous loads.
The US manufacturer Otis is installing 54 high-performance elevators in the tower to quickly transport the high-rise residents to their luxurious apartments. The fastest lift in the world will go up at 65 kilometers per hour. The occupants will hardly notice the speed. Because the cabs will accelerate and brake gently. In addition, there is automatic pressure equalization, just like in an airplane.
But with all the superlatives with which the Burj Dubai shows off - the hunt for records continues. Security chief Mahmed can hardly wait for the 1000-meter colossus Al Burj to go into construction. “I would then like to be there,” he says.
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